(પ.ક્ર. : $Fe=26, Co= 27, Ni =28, Pt= 78$)
${\left[ Ni ( CN )_4\right]^{2-},\left[ Ni ( CO )_4\right],\left[ NiCl _4\right]^{2-}}$
${\left[ Fe ( CN )_6\right]^{4-},\left[ Cu \left( NH _3\right)_4\right]^{2+}}$
${\left[ Fe ( CN )_6\right]^{3-} \text { and }\left[ Fe \left( H_2O\right)_6\right]^{2+}}$
(આપેલ પરમાણુ ક્રમાંક $: V, 23; Cr, 24, Fe, 26 Ni, 28)$
$V ^{3+}, Cr ^{3+}, Fe ^{2+}, Ni ^{3+}$